Screen printing process and machine

Abstract

In a screen printing process and machine for stepwise printing a succession of images, the screen printing stencil is moved along with the material during the printing operation, while the material is supported by a rotatable backing roller against the force applied to the material by the screen and a doctor blade disposed opposite the backing roller. During the printing operation the material is rolled against the stencil by the backing roller which together with the doctor may be moved in the opposite direction to the stencil. The direction of movement of the backing roller and an upstream guide roller, relative to the direction of movement of the stencil, is such as to promote separation of the material after printing from the stencil.

What is claimed is: 
     
       1. In a screen printing process for the stepwise printing of a succession of images on a longitudinally moving material by means of a printing mechanism comprising a printing stencil, an associated doctor adjacent one surface of said stencil, and a counter-pressure backing roller adjacent the other surface of said stencil opposite said one surface of said stencil, wherein the material to be printed upon is passed between said stencil and said backing roller so as to extend part way around said roller, wherein said stencil is moved downwardly onto said material for printing thereon and during said printing is moved with said material from a starting position to a final position relative to said doctor, the doctor pressing print medium through said stencil onto said material during said movement and said material being rolled against said stencil by said backing roller during said movement, wherein said stencil and said doctor are lifted from said material and returned to their relative starting position after each printing operation, wherein said doctor and said backing roller are displaced synchronously with respect to said stencil and in the opposite direction to the direction of motion of said material issuing from said backing roller, and wherein said stencil is substantially horizontal; the improvement wherein a portion of said material passing to said printing mechanism and a portion of said material issuing from said backing roller are moved parallel to each other and downwardly at an acute angle relative to said stencil, and wherein said printing mechanism is moved, at least during said printing, parallel to said portions of said material.   
     
     
       2. A process as set forth in claim 1 wherein said portions of said material are moved at an angle of substantially 15° relative to said stencil. 
     
     
       3. In a screen printing apparatus for the stepwise printing of a succession of images on a material, comprising: a printing mechanism comprising a stencil, a doctor adjacent one surface of said stencil, and a counter-pressure backing roller adjacent the other surface of said stencil opposite said one surface of said stencil;   means for passing said material into and through said printing mechanism, between said stencil and said counter-pressure backing roller so as to extend part way around said roller;   means for moving said stencil downwardly onto said material for printing on said material, and means for moving said stencil along with said material during said printing, from a starting position to a final position with respect to said doctor, the doctor pressing printing medium through said stencil onto said material, and said backing roller rolling said material against said other surface of said stencil during said printing;   means for lifting said stencil and said doctor from said material and returning them to their starting position after said printing;   means for displacing said doctor and said backing roller synchronously with respect to said stencil and in the opposite direction to the direction of moving of said material issuing from said backing roller, said stencil being substantially horizontal;   the improvement comprising means for guiding a portion of said material passing into said printing mechanism and a portion thereof issuing from said backing roller so that they move parallel to each other and downwardly at an acute angle relative to said stencil, said apparatus comprising means for moving said printing mechanism in a direction parallel to said portions of said material at least during said printing.   
     
     
       4. Apparatus as set forth in claim 3 including means for adjusting the distance by which said doctor and said backing roller are displaced with respect to the stencil. 
     
     
       5. Apparatus as set forth in claim 4 and further including a material guide roll disposed upstream of said backing roller and movable with said doctor and said backing roller within the adjusted limits of their movement. 
     
     
       6. Apparatus as set forth in claim 3 including means for adjusting the distance between said starting and final positions of said stencil. 
     
     
       7. Apparatus as set forth in claim 3 including means for rotating said backing roller at a speed dependent on the speed at which said backing roller is displaceable relative to said material. 
     
     
       8. Apparatus as set forth in claim 3, said printing mechanism further including a material guide roller disposed upstream of said backing roller, said backing roller and said guide roller being so disposed that the portion of said material which issues from said backing roller and the portion of said material which passes to said guide roller are offset relative to each other but parallel to each other and are at an acute angle to the horizontal. 
     
     
       9. Apparatus as set forth in claim 3 including an adjustable drive transmission means for moving said material. 
     
     
       10. Apparatus as set forth in claim 3, comprising common mounting means carrying said doctor and said backing roller. 
     
     
       11. Apparatus as set forth in claim 10 wherein said common mounting means is a first carriage. 
     
     
       12. Apparatus as set forth in claim 10 and further including a material guide roller disposed upstream of said backing roller and also carried by said common mounting means. 
     
     
       13. Apparatus as set forth in claim 10 including guide means for displaceably mounting said mounting means and extending parallel to said portions of material. 
     
     
       14. Apparatus as set forth in claim 13 and further including: a second mounting means for carrying said stencil; and second guide means disposed on said common mounting means and supporting said second mounting means for reciprocating movement on said common mounting means, said second guide means extending parallel to the plane of said stencil. 
     
     
       15. Apparatus as set forth in claim 14 wherein said second mounting means is a carriage. 
     
     
       16. Apparatus as set forth in claim 14 wherein said common mounting means forms an opening and said second guide means is arranged within said opening. 
     
     
       17. Apparatus as set forth in claim 14 wherein said second mounting means forms an elongate opening which extends normal to said second guide means, and further including means for driving said second mounting means, comprising: a pivotally mounted lever having first and second arms, a drive member mounted on the first arm of the lever at a position spaced from its pivot mounting, a cam follower mounted on the second arm of a lever at a position spaced from its pivot mounting, and cam means with which said cam follower co-operates and whose configuration determines the desired movement to be imparted to said stencil. 
     
     
       18. Apparatus as set forth in claim 17 wherein said cam means is a cam surface provided on a rotary member. 
     
     
       19. Apparatus as set forth in claim 17 wherein said means for driving said second mounting means includes an adjustable means for varying the driving of said second mounting means. 
     
     
       20. Apparatus as set forth in claim 17 wherein said means for driving said second mounting means includes an interchangeable means for varying the driving of said second mounting means. 
     
     
       21. Apparatus as set forth in claim 13 wherein said common mounting means forms an opening which extends normal to said guide means, and further including means for driving said common mounting means, including a drive member and transmission means connecting said drive member to said common mounting means. 
     
     
       22. Apparatus as set forth in claim 21 wherein said drive member comprises a crank arm. 
     
     
       23. Apparatus as set forth in claim 22 wherein said second mounting means forms an elongate opening which extends normal to said second guide means, and further including means for driving said second mounting means, comprising: a pivotally mounted lever having first and second arms, a drive member mounted on the first arm of the lever at a position spaced from its pivot mounting, a cam follower mounted on the second arm of a lever at a position spaced from its pivot mounting, and a rotary member comprising cam means with which said cam follower co-operates and whose configuration determines the desired movement to be imparted to said stencil, wherein said crank arm is mounted rotatably and adjustably on said rotary member. 
     
     
       24. Apparatus as set forth in claim 19 wherein said means for driving said common mounting means includes an adjustable means for varying the driving of said common mounting means. 
     
     
       25. Apparatus as set forth in claim 21 wherein said means for driving said common mounting means includes an interchangeable means for varying the driving of said common mounting means. 
     
     
       26. Apparatus as set forth in claim 3 and further including a material guide roller disposed upstream of said backing roller, and means for rotating said guide roller at a speed dependent on the speed at which said guide roller is displaceable relative to said material. 
     
     
       27. Apparatus as set forth in claim 26 including at least first and second drive guide rollers for said material, which drive guide rollers are each arranged at a spacing from the assembly of said doctor, backing roller and stencil and which each have a drive shaft, and further including respective drive wheels on each of said shafts and a common flexible elongate drive means drivingly interconnecting all said drive wheels, the flexible drive means having a portion which extends along a region which is parallel to the path of movement of said material and in which said flexible drive means moves in the opposite direction to the movement of said material. 
     
     
       28. Apparatus as set forth in claim 27 wherein said flexible drive means comprises a chain and said drive wheels are gears.